1. Sentence and define vocabulary for chapter 27.1
What will I learn Today? I will be able to describe how astronomers determine the composition and surface temperature of a star
Standards
Students know the Sun is a typical star and is powered by nuclear reactions, primarily the fusion of hydrogen to form helium.
Students know the evidence indicating that the planets are much closer to Earth than the stars are.
Homework
Sentence and define vocabulary for chapter 27.1

2. Chapter 27.1 Vocabulary Star circumpolar Red shift Light years
Parallax
Apparent magnitude
Absolute magnitude
H-R diagram
Main sequence stars
Giants
Supergiants
White dwarfs

3. Chapter 27.1 Notes Characteristics of stars
The sun is our closest star
A star is a body of gas that gives off a tremendous amount of light and heat
From earth stars look like tiny white lights, but if you look closely they shine different colors (blue, yellow, orange, red and white)
Stars also vary in mass and composition

4. Chapter 27.1 Notes Composition and temperature
The light of stars is analyzed through a spectrometer, which breaks the light into different wavelengths or colors
The display of colors and lines is called the spectrum
There are three types of spectra; emission (bright light), Absorption (dark line) and continuous

6. Chapter 27.1 Notes Composition and temperature
The dark lines are what tell us what makes up a star, the types of materials that can found in the star
Stars are mainly Hydrogen and Helium, but also have carbon, oxygen, nitrogen, and calcium
The temperature range of stars is 2,800c to 24,000c, with some blue stars reaching 50,000c

8. Chapter 27.1 Notes
Motion
There are two types of motion with stars apparent and actual
Actual motion can be seen with only high powered telescopes, because of the great distances
Apparent motion can be seen every night as you see stars move across the sky
Stars also appear to shift as our seasons change or as we move around the sun they become visible to us

9. Chapter 27.1 Notes
Motion
There are some stars that seem to always be out or never drop below the horizon, these are the circumpolar or the little dipper
Star have three actual motions
First they turn on there axis
Second, most rotate around another star
Third, they move toward or away from earth
Light has a Doppler effect just like sound
Blue means, it is moving closer to you
Red means, it is moving farther away from you

10. Chapter 27.1 Notes Distance to the stars
Star distance is measured in light-years
Light travels at 300,000 km/s or in one year 9.5 trillion miles
The closest star is Proxima Centauri at 4.2 light years, Sirius the brightest star is 9 light years, and Polaris or Northern Star is 700 light years away
Distance is measured using a process known as parallax
The shift of a star from January to June can be used to determine distance to within 1,000 light years
The closer a star is the bigger the shift

11. Chapter 27.1 Notes Distance to the stars
Another method is to use the brightness of stars – for more distance stars
They estimate the true brightness by using the spectrum
They then compare it to its apparent brightness
Cepheid are stars that pulse in brightness on a cycle of time
From 1 day to 100 days
The longer the cycle the brighter the star

12. Chapter 27.1 Notes We can see about 6,000 stars with our eyes
Stellar Magnitudes
We can see about 6,000 stars with our eyes
A good telescope will allow you to see about 3,000,000,000 (billion) stars
The Hubble telescope can see about 1,000,000,000,000 (Trillion) stars
Stars are broken into two different scales, how bright they appear from earth and the other measure is how bright they would be if all stars were the same distance

13. Chapter 27.1 Notes Apparent Magnitude
This is how bright a star appears from earth
Object mV
Sun
-26.8
Full Moon
-12.5
Venus at brightest
-4.4
Jupiter at brightest
-2.7
Sirius
-1.47
Vega
0.04
Betelgeuse
0.41
Polaris
1.99
Naked eye limit 6
Pluto
15.1
Hubble Space Telescope 31

14. Chapter 27.1 Notes Absolute Magnitude
This is how bright the star would be if it was 32.6 light years away from the earth
If we take the sun with an apparent magnitude of and moved it 32.6 light years away, it would have an absolute magnitude of +5
So if the apparent is less (-26.8) then the absolute (+5) the star is closer then 32.6 light years
If the apparent is (+6) more then the absolute (+2) the star is farther then 32.6 light years
3.26 is one parsec – a star that has a parallax of one second

15. Chapter 27.1 Notes
Classification of stars

16. Chapter 27.1 Notes
Classification of stars
When you classify stars by there temperatures and absolute magnitude a pattern develops
The line through the graph is called the main sequence of stars, most stars visible at night are in this group
It starts in the lower right hand corner with cool, dim and red stars
It then moves up to the upper left corner with hot, bright, and blue stars
The upper right is cool bright stars
The lower left are hot and dim stars, called white dwarfs (about the size of earth)

17. Chapter 27 activity Procedure
Stand directly in front of and directly facing the red cup at a distance of several meters.
Close one eye and sketch the position of the red cup relative to the background and white cups.
Take several steps back and to the right of your original position, repeat step 2
Take several steps directly back and make another sketch.
Repeat step 4 once again.

18. Chapter 27 activity - analysis
Compare your drawings. Did the red cup change position as you viewed it from different locations? Explain
What kind of results would you expect if you continued to repeat step 5 at greater and greater distances? Explain
If you noted the positions of several stars with a powerful telescope, what would you expect to observe about their positions if you sighted the same stars several months later? Explain

19. Chapter 27.2 Vocabulary Nebula Protostar Planetary nebula Novas
Supernova
Neutron star
Pulsars
Black hole

20. Chapter 27.2 Notes Stellar Evolution Nebula – a cloud of gas and dust
Protostar – a shrinking spinning region of gas that flattens into a disk with a central concentration
Stars exists for billions of years. Stars form in nebula that usually are composed of 70% hydrogen, 28% helium, and 2% heavier materials.
Gravity pulls it all together. Matter gets warmer with increased pressure, Over millions years, until 10,000,000C fusion begins. More than one star can form, as well as planets

21. Chapter 27.2 Notes Main Sequence stars
Second and longest stage of a stars life
Energy generated in the core through fusion of hydrogen into helium, 1g of hydrogen can generate enough power to keep a 100 watt bulb burning for 3,000 years.
The energy bubbles upward like boiling water, gravity prevents the expansion of the star.
These two forces keep the star at a stable size, as long as it has enough hydrogen to convert to helium.

22. Chapter 27.2 Notes Third stage of a stars life
Giants & Supergiant
Third stage of a stars life
All atoms of hydrogen have fused into helium; therefore the core will contract under the force of gravity.
Temp increases and helium fusion begins, carbon formed
Hydrogen fusion continues in the areas surrounding the core and the star expands into a giant: 10 or more times larger then our sun, a supergiant is 100 times

23. Chapter 27.2 Notes
White Dwarf Stars
Planetary nebula – a expanding shell of gas left from a dying star.
The end of helium fusion is the end of the giant stage of a medium size star.
The outer gas layers are lost and the core revealed, it will heat and illuminate the expanding gases.
It takes billions of years for a white dwarf to cool into a black or brown dwarf, the universe is too young to have any in it yet.

24. Chapter 27.2 Notes
Novas
Nova – a white dwarf that explodes as it cools, becoming a thousand times brighter for a short time.
Some white dwarfs do not just cool, they have one or more large explosions.
Astronomers think this may be caused by a companion star that is having material taken from it by the white dwarf.

25. Chapter 27.2 Notes
Supernovas
Supernova – a star that explodes with such tremendous force that it blows itself apart.
A star with 10 to 100 times of our sun and the explosions can be 100 times brighter than novas.
They can release as much energy as our sun would over 500 million years.
These massive stars continue to fuse heavier materials until the core turns into iron, this core then contracts from gravity and explodes

26. Chapter 27.2 Notes
Neutron Stars
Neutron star – an extremely small and dense ball of neutrons.
Pulsars – two beams of radiation that sweep across space like a lighthouse
Formed from a supernova, as the star collapses only neutrons are left. A spoonful would weigh 100 million tons on earth
Some give off radiation at the poles called pulsars, we can detect these as radio waves.

27. Chapter 27.2 Notes
Black Holes
Black hole – a hole in space with such gravity that light can not escape
The most massive stars form black holes
They are invisible to the eye, astronomers look for companion stars that are influenced by the gravity or the energy of the materials being pulled into the Black Hole
Massive Black holes may be at the center of galaxies.

28. Chapter 27.3 Vocabulary Constellations Galaxies Spiral galaxy
Barred spiral galaxy
Elliptical galaxy
Irregular galaxy
Open cluster
Globular clusters
Binary stars
Quasars

29. Chapter 27.3 Notes
Star Groups
Constellations
You see what appear to be single stars, yet only 1 in 4 is actually a single star. 1/3 are double and the rest are triple or more star groups or clusters.
Constellation – a pattern of stars
There are 88 recognized constellation.
They are used as a star locator map, the star are labeled by apparent magnitude and the constellation they appear in.
Some stars are bright enough to have been given their own names - Antares

30. Chapter 27.3 Notes Galaxy – A large scale group of stars
Galaxies
Galaxy – A large scale group of stars
The major component of the universe, a typical galaxy is 100,000 light years in diameter and has about 100 billion stars.
Galaxies also contain gas and dust or nebulae, some are bright because they reflect light or from the gas within them. The dark areas absorb light from distant stars.
Estimates of 50 billion to 1 trillion galaxies in the known universe.

31. Chapter 27.3 Notes
Galaxies
Types of Galaxies
The two closest to the Milky Way is the large Magellanic Cloud and the small Magellanic Cloud at 150,000 light years
There are 17 other galaxies within 3 million light years and this makes up the Local Group.
Spiral galaxy -
Barred spiral galaxy -
Elliptical galaxy -
Irregular galaxy -

32. Chapter 27.3 Notes The Milky Way
Our sun is one of billions stars that circle the galactic center. It is 2,000 light years thick at the center.
We are 30,000 light years from the center in a spiral arm.
We revolve around the center at 250km/s, it takes 200 million years to complete a revolution

33. Chapter 27.3 Notes Star Cluster Binary stars Open clusters -
Globular clusters -
Difference – globular clusters have more stars, are in the core of the galaxy and a spherical shape. Open cluster are a loose grouping and are in the spiral arms.
Binary stars -
Used to determine stellar mass
Consist of two stars, a multiple star system has more then two in orbit around each other.

34. Chapter 27.3 Notes Formation of the Universe
The big bang theory – that the universe formed from a single point of matter.
Then 12 to 15 billion years ago the “Big Bang” occurred propelling matter and energy outward in all directions.
As they moved away from the center gravity began to have an effect and formed galaxies
Quasars –
These may be the oldest objects in our universe